Reindexing table?

Any details about filter expression and locate expression?

>This is a new one on me.
>
>a mature FP2.6a DOS app crashed this pm with the bizarre error "Meaningless Expression" which I've never seen before for ANY error in Fox!
>
>Furthermore it was not an unusual situation. A filter has been set, we do a "Locate" to see if there are any records. If not we move on. Or we used to until this happened. Now, if there are no records in the filter, we get the aforementioned error message.
>
>Clues anybody?